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chriz74

How do you reduce a plastic crystal diameter easily?

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I had to reduce the diameter of a sternkreuz glass from 30.3mm to 30mm or the retainer ring of the watch wouldn't fit. To do so I used sandpaper by hand (very tiring and time consuming) and for the final part I used the dremel with a sanding tip. Then I used the dremel and polywatch to polish.

Do you use a lathe to do this kind of job?

I thought if I could put the glass on the dremel maybe with a sucker then the process would be a lot faster and easier. I have another one that I want to try but by hand is too long.

advices?

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Did you do anything to solve?

Nothing tried yet. But I was going to use a lathe chuck to hold the crystal and chuck it in a variable speed drill and spin it while holding a sanding stick to the edge. Have not validated the theory yet so can't recommend


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You can order a 3 or 3.1 crystal ,...or as you suggested , try to use a sucker in a drill or dremel . I had a similar situation where I wanted to turn a case back to put a finish on it and I got a small sucker from ebay that is used to prop a cell phone for viewing . I also went to the hardware store and Wal-mart and looked at the clear plastic suckers that are used on bathroom and kitchen racks .

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7 hours ago, chriz74 said:

How did you attach the sucker to a dremel head?

Well , for mine ,  the sucker head to prop a smart phone had a wooden dowel that I attached to a drill . But the ones for bathroom racks have small gauge wire for the racks that can be cut and installed in a larger dremel collet....I think.

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20mm sucker on a drill worked. Advice: make it turn slow or the sandpaper will sand less efficiently. After sanding I put polywatch on cotton and polished in the same way, with the drill spinning the glass.

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Hi,

You might have it all sorted by now, but I have used this successfuly in the past. This is if you have a lathe.

(Hope that link copied over)

You do have to fiddle a bit to get the crystal central, but if you keep the speed slow it is not crucial. The other tip is to use the file across the work and not aligned with it. I learnt the hard way that crystals will be easily scratched if the file slips off the work. The plus side is that the crystal remains circular and you dont seem to compromise its fit as I think you would do with a dremel of sandpaper. The suction cup seems simple and a good idea too.

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Update. I discovered an easy way. I just polish the outer diameter on my buffer that I use for case polishing. Very gentle and worked like a champ. I just spin the crystal around as I go and it remained perfectly concentric. I just kept checking with a caliper.


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